add missing GroupedFieldSet type

Author: yaacovCR

src/execution/execute.ts

@@ -471,7 +471,7 @@ function executeFields(
   parentType: GraphQLObjectType,
   sourceValue: unknown,
   path: Path | undefined,
-  fields: Map<string, FieldGroup>,
+  fields: GroupedFieldSet,
 ): PromiseOrValue<ObjMap<unknown>> {
   const results = Object.create(null);
   let containsPromise = false;